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</a></div> <!----></nav>  <ul class="sidebar-links"><li><a href="/fe/" aria-current="page" class="sidebar-link">大前端学习路径 + B站资源整合</a></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>HTML</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading open"><span>CSS</span> <span class="arrow down"></span></p> <ul class="sidebar-links sidebar-group-items"><li><a href="/fe/css/" aria-current="page" class="sidebar-link">目录</a></li><li><a href="/fe/css/flexbox.html" class="sidebar-link">Flexbox 弹性布局</a></li><li><a href="/fe/css/box_model.html" class="sidebar-link">面试官：说说你对盒子模型的理解?</a></li><li><a href="/fe/css/selector.html" class="sidebar-link">面试官：css选择器有哪些？优先级？哪些属性可以继承？</a></li><li><a href="/fe/css/em_px_rem_vh_vw.html" class="sidebar-link">面试官：说说em/px/rem/vh/vw区别?</a></li><li><a href="/fe/css/dp_px_dpr_ppi.html" class="sidebar-link">面试官：说说设备像素、css像素、设备独立像素、dpr、ppi 之间的区别？</a></li><li><a href="/fe/css/hide_attributes.html" class="sidebar-link">面试官：css中，有哪些方式可以隐藏页面元素？区别?</a></li><li><a href="/fe/css/BFC.html" class="sidebar-link">面试官：谈谈你对BFC的理解？</a></li><li><a href="/fe/css/center.html" class="sidebar-link">面试官：元素水平垂直居中的方法有哪些？如果元素不定宽高呢？</a></li><li><a href="/fe/css/column_layout.html" class="sidebar-link">面试官：如何实现两栏布局，右侧自适应？三栏布局中间自适应呢？</a></li><li><a href="/fe/css/grid.html" class="sidebar-link">面试官：介绍一下grid网格布局</a></li><li><a href="/fe/css/css3_features.html" class="sidebar-link">面试官：CSS3新增了哪些新特性？</a></li><li><a href="/fe/css/animation.html" class="sidebar-link">面试官：css3动画有哪些？</a></li><li><a href="/fe/css/reflow_repaint.html" class="sidebar-link">面试官：怎么理解回流跟重绘？什么场景下会触发？</a></li><li><a href="/fe/css/responsive_layout.html" class="sidebar-link">面试官：什么是响应式设计？响应式设计的基本原理是什么？如何做？</a></li><li><a href="/fe/css/css_performance.html" class="sidebar-link">面试官：如果要做优化，CSS提高性能的方法有哪些？</a></li><li><a href="/fe/css/single_multi_line.html" class="sidebar-link">面试官：如何实现单行／多行文本溢出的省略样式？</a></li><li><a href="/fe/css/visual_scrolling.html" class="sidebar-link">面试官：如何使用css完成视差滚动效果?</a></li><li><a href="/fe/css/triangle.html" class="sidebar-link">面试官：CSS如何画一个三角形？原理是什么？</a></li><li><a href="/fe/css/less_12px.html" class="sidebar-link">面试官：让Chrome支持小于12px 的文字方式有哪些？区别？</a></li><li><a href="/fe/css/sass_less_stylus.html" class="sidebar-link">面试官：说说对Css预编语言的理解？有哪些区别?</a></li><li><a href="/fe/css/css.html" aria-current="page" class="active sidebar-link">CSS</a><ul class="sidebar-sub-headers"></ul></li></ul></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>JavaScript</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>TypeScript</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>ES6</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Vue</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Vue3</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>React</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Webpack</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Node.js</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>性能优化</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>手写代码</span> <span class="arrow right"></span></p> <!----></section></li></ul> </aside> <main class="page"> <div class="theme-default-content content__default"><h1 id="css"><a href="#css" class="header-anchor">#</a> CSS</h1> <h3 id="目录"><a href="#目录" class="header-anchor">#</a> 目录</h3> <ul><li>[x] 1. 使用css，让一个div消失在视野中</li> <li>[x] 2. display属性值都有哪些</li> <li>[x] 3. 盒子水平垂直居中</li> <li>[x] 4. CSS3盒模型</li> <li>[x] 5. 几大经典布局</li> <li>[x] 6. 移动端响应式布局解决方案</li> <li>[x] 7. z-index 的工作原理</li> <li>[x] 8. 文字垂直居中且可自适应</li> <li>[x] 9. CSS渲染性能</li></ul> <h3 id="_4-position-sticky"><a href="#_4-position-sticky" class="header-anchor">#</a> 4. position: sticky</h3> <ul><li><a href="https://www.zhangxinxu.com/wordpress/2018/12/css-position-sticky/" target="_blank" rel="noopener noreferrer">杀了个回马枪，还是说说position:sticky吧<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></li></ul> <p>sticky元素效果完全受制于父级元素们。</p> <p>特性表现：</p> <ol><li>父级元素不能有任何overflow:visible以外的overflow设置，否则没有粘滞效果。</li> <li>父级元素 同 粘性定位元素等高，则没有粘滞效果。</li> <li>同一个父容器中的sticky元素，如果定位值相等，则会重叠；如果属于不同父元素，且这些父元素正好紧密相连，则会鸠占鹊巢，挤开原来的元素，形成依次占位的效果。</li> <li>sticky定位，可以设置 <code>top</code> / <code>right</code> / <code>bottom</code> / <code>left</code>四个值。</li></ol> <h3 id="_11-如果设计中使用了非标准的字体-你该如何去实现"><a href="#_11-如果设计中使用了非标准的字体-你该如何去实现" class="header-anchor">#</a> 11. 如果设计中使用了非标准的字体，你该如何去实现？</h3> <p>所谓的标准字体是多数机器上都会有的，或者即使没有也可以由默认字体替代的字体。</p> <p>方法：</p> <ol><li>用图片代替
web fonts在线字库，如Google Webfonts，Typekit等等；网页链接...；</li> <li>@font-face，Webfonts(字体服务例如：Google Webfonts，Typekit等等。)</li></ol> <h3 id="_12-常见的浏览器兼容问题"><a href="#_12-常见的浏览器兼容问题" class="header-anchor">#</a> 12. 常见的浏览器兼容问题？</h3> <ol><li>不同浏览器的标签默认的内.外补丁不同。*{margin:0;padding:0;}</li> <li>图片默认有间距。使用float属性为img布局</li> <li>居中问题（而FF默认为左对齐）。margin: 0 auto;</li> <li>CSS 兼容前缀</li></ol> <div class="language- extra-class"><pre class="language-text"><code>-ms- IE
-moz- Firefox
-o- Opera
-webkit- Chrome
</code></pre></div><ol start="5"><li>使用CSS Hack。如： +:IE6,7的前缀，-:IE6的前缀</li></ol> <h3 id="_13-z-index"><a href="#_13-z-index" class="header-anchor">#</a> 13. z-index</h3> <ul><li><a href="https://www.zhangxinxu.com/wordpress/2016/01/understand-css-stacking-context-order-z-index/" target="_blank" rel="noopener noreferrer">深入理解CSS中的层叠上下文和层叠顺序<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></li></ul> <h4 id="_13-1-层叠上下文-stacking-context"><a href="#_13-1-层叠上下文-stacking-context" class="header-anchor">#</a> 13.1 层叠上下文（stacking context）</h4> <p><strong>层叠上下文</strong>是HTML中一个三维的概念。每个盒模型的位置是三维的，分别是平面画布上的 <code>X轴</code>，<code>Y轴</code> 以及表示层叠的 <code>Z轴</code>。离屏幕观察者更近。</p> <h4 id="_13-2-层叠等级-stacking-level"><a href="#_13-2-层叠等级-stacking-level" class="header-anchor">#</a> 13.2 层叠等级（stacking level）</h4> <p>概念：</p> <ul><li>在同一个层叠上下文中，它描述定义的是该层叠上下文中的元素在 <code>Z</code> 轴上的上下顺序。</li> <li>在其他普通元素中，它描述定义的是这些普通元素在Z轴上的上下顺序。</li></ul> <h4 id="_13-3-层叠顺序-stacking-order"><a href="#_13-3-层叠顺序-stacking-order" class="header-anchor">#</a> 13.3 层叠顺序（stacking order）</h4> <p><strong>层叠顺序</strong>表示元素发生层叠时按照特定的顺序规则在Z轴上垂直显示</p> <p><strong>由此可见，前面所说的“层叠上下文”和“层叠等级”是一种概念，而这里的“层叠顺序”是一种规则。</strong></p> <h3 id="_14-css-预处理器"><a href="#_14-css-预处理器" class="header-anchor">#</a> 14. CSS 预处理器</h3> <ul><li><p><a href="https://aotu.io/notes/2019/10/29/css-preprocessor/index.html" target="_blank" rel="noopener noreferrer">2019年，你是否可以抛弃 CSS 预处理器？<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a> <strong>CSS 预处理器</strong> 是一个能让你通过预处理器自己独有的语法来生成 CSS 的程序。</p></li> <li><p><code>Sass</code>：2007 年诞生，最早也是最成熟的 CSS 预处理器，拥有 Ruby 社区的支持和 Compass 这一最强大的 CSS 框架，目前受 LESS 影响，已经进化到了全面兼容 CSS 的 SCSS。</p></li> <li><p><code>Less</code>：2009年出现，受 SASS 的影响较大，但又使用 CSS 的语法，比起 SASS 来，可编程功能不够，不过优点是简单和兼容 CSS，反过来也影响了 SASS 演变到了 SCSS 的时代。Bootstrap 就是采用 LESS 做底层语言的。</p></li> <li><p><code>Stylus</code>：2010 年产生，来自 Node.js 社区，主要用来给 Node 项目进行 CSS 预处理支持</p></li></ul> <ol><li>优点：变量（variables），代码混合（ mixins），嵌套（nested rules）以及 代码模块化(Modules)。</li> <li>缺点：
<ul><li>额外的编译配置</li> <li>编译成本。每次修改代码都需要重新编译,占用时间和 CPU。</li> <li>学习成本。不同的 CSS 预处理器语法不同，增加学习成本</li></ul></li></ol> <h3 id="_1-使用css-让一个div消失在视野中"><a href="#_1-使用css-让一个div消失在视野中" class="header-anchor">#</a> 1. 使用css，让一个div消失在视野中？</h3> <ol><li>display：none;</li> <li>visibility：hidden;</li> <li>ocpacity：0;</li> <li>height: 0;</li> <li>filter: opacity(0);（不兼容IE）— <a href="https://www.runoob.com/cssref/css3-pr-filter.html" target="_blank" rel="noopener noreferrer">filter滤镜<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a>：对比度、饱和度、阴影、色相、透明度</li></ol> <h3 id="_2-display属性值都有哪些"><a href="#_2-display属性值都有哪些" class="header-anchor">#</a> 2. display属性值都有哪些？</h3> <p>display: none、block、inline、inline-block、list-item、table、table-cell、inherit、flex......;</p> <ul><li>display: none
<ul><li>使用css，让一个div消失在视野中？</li> <li>display: none 和 visibility: hidden 的区别？</li> <li>opacity 的兼容处理？</li> <li>filter还能做哪些事情？</li></ul></li> <li>display: flex; — CSS3 弹性盒子(Flex Box)
<ul><li>项目中什么时候用到了flex？</li> <li>还有哪些居中方式？</li> <li>响应式布局还可以怎么做？</li> <li>盒子模型都有哪些？</li></ul></li></ul> <h3 id="_3-盒子水平垂直居中"><a href="#_3-盒子水平垂直居中" class="header-anchor">#</a> 3. 盒子水平垂直居中</h3> <p>回答技巧：最开始xxx，喜欢用flex，后来发现xxx，在xx博客上突然发现xx更好，xx解决了兼容性（拒绝背书式）</p> <ul><li>定位：三种</li> <li>display: flex</li> <li>JavaScript</li> <li>display: table-cell</li></ul> <p>（1）知道具体宽高</p> <div class="language-scss extra-class"><pre class="language-scss"><code><span class="token selector">.box </span><span class="token punctuation">{</span>
    <span class="token property">width</span><span class="token punctuation">:</span> 100px<span class="token punctuation">;</span>
    <span class="token property">height</span><span class="token punctuation">:</span> 50px<span class="token punctuation">;</span>
    <span class="token property">positon</span><span class="token punctuation">:</span> absolute<span class="token punctuation">;</span>
 <span class="token property">top</span><span class="token punctuation">:</span> 50%<span class="token punctuation">;</span>
 <span class="token property">left</span><span class="token punctuation">:</span> 50%<span class="token punctuation">;</span>
 <span class="token property">margin-top</span><span class="token punctuation">:</span> -25px<span class="token punctuation">;</span>
 <span class="token property">margin-left</span><span class="token punctuation">:</span> -50px<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre></div><p>（2）有宽高限制</p> <div class="language-scss extra-class"><pre class="language-scss"><code><span class="token selector">.box </span><span class="token punctuation">{</span>
    <span class="token property">width</span><span class="token punctuation">:</span> 100px<span class="token punctuation">;</span>
    <span class="token property">height</span><span class="token punctuation">:</span> 50px<span class="token punctuation">;</span>
 <span class="token property">position</span><span class="token punctuation">:</span> absolute<span class="token punctuation">;</span>
 <span class="token property">top</span><span class="token punctuation">:</span> 0<span class="token punctuation">;</span>
 <span class="token property">right</span><span class="token punctuation">:</span> 0<span class="token punctuation">;</span>
 <span class="token property">bottom</span><span class="token punctuation">:</span> 0<span class="token punctuation">;</span>
 <span class="token property">left</span><span class="token punctuation">:</span> 0<span class="token punctuation">;</span>
 <span class="token property">margin</span><span class="token punctuation">:</span> auto<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre></div><p>（3）没有宽高限制（兼容IE9+）</p> <div class="language-scss extra-class"><pre class="language-scss"><code><span class="token selector">.box </span><span class="token punctuation">{</span>
 <span class="token property">position</span><span class="token punctuation">:</span> absolute<span class="token punctuation">;</span>
 <span class="token property">top</span><span class="token punctuation">:</span> 50%<span class="token punctuation">;</span>
 <span class="token property">left</span><span class="token punctuation">:</span> 50%<span class="token punctuation">;</span>
 <span class="token property">transform</span><span class="token punctuation">:</span> <span class="token function">translate</span><span class="token punctuation">(</span>-50%<span class="token punctuation">,</span> -50%<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre></div><p>（4）Flex弹性盒模型（兼容IE10+）</p> <div class="language-scss extra-class"><pre class="language-scss"><code><span class="token selector">.father </span><span class="token punctuation">{</span>
 <span class="token property">display</span><span class="token punctuation">:</span> flex<span class="token punctuation">;</span>
 <span class="token property">justify-content</span><span class="token punctuation">:</span> center<span class="token punctuation">;</span> <span class="token comment">/* x轴 */</span>
 <span class="token property">align-items</span><span class="token punctuation">:</span> center<span class="token punctuation">;</span> <span class="token comment">/* y轴 */</span>
<span class="token punctuation">}</span>
</code></pre></div><p>（5）js实现，就是模拟css写样式</p> <div class="language-javascript extra-class"><pre class="language-javascript"><code><span class="token keyword">const</span> <span class="token constant">HTML</span> <span class="token operator">=</span> document<span class="token punctuation">.</span>documentElement<span class="token punctuation">,</span>
   winW <span class="token operator">=</span> <span class="token constant">HTML</span><span class="token punctuation">.</span>clientWidth<span class="token punctuation">,</span>
   winH <span class="token operator">=</span> <span class="token constant">HTML</span><span class="token punctuation">.</span>clientHeight<span class="token punctuation">,</span>
   boxW <span class="token operator">=</span> box<span class="token punctuation">.</span>offsetWidth<span class="token punctuation">,</span>
   boxH <span class="token operator">=</span> box<span class="token punctuation">.</span>offsetHeight<span class="token punctuation">;</span>
   box<span class="token punctuation">.</span>style<span class="token punctuation">.</span>positon <span class="token operator">=</span> <span class="token string">&quot;absolute&quot;</span><span class="token punctuation">;</span>
   box<span class="token punctuation">.</span>style<span class="token punctuation">.</span>left <span class="token operator">=</span> <span class="token punctuation">(</span>winW <span class="token operator">-</span> boxW<span class="token punctuation">)</span> <span class="token operator">/</span> <span class="token number">2</span> <span class="token operator">+</span> <span class="token string">&quot;px&quot;</span><span class="token punctuation">;</span>
   box<span class="token punctuation">.</span>style<span class="token punctuation">.</span>top <span class="token operator">=</span> <span class="token punctuation">(</span>winH <span class="token operator">-</span> boxH<span class="token punctuation">)</span> <span class="token operator">/</span> <span class="token number">2</span> <span class="token operator">+</span> <span class="token string">&quot;px&quot;</span><span class="token punctuation">;</span>
</code></pre></div><p>（6）固定宽高</p> <div class="language-scss extra-class"><pre class="language-scss"><code><span class="token selector">.father </span><span class="token punctuation">{</span>
 <span class="token property">width</span><span class="token punctuation">:</span> 500px<span class="token punctuation">;</span>
 <span class="token property">height</span><span class="token punctuation">:</span> 500px<span class="token punctuation">;</span>
 <span class="token property">display</span><span class="token punctuation">:</span> table-cell<span class="token punctuation">;</span>
 <span class="token property">vertical-align</span><span class="token punctuation">:</span> middle<span class="token punctuation">;</span>
 <span class="token selector">text-align: center
    .box </span><span class="token punctuation">{</span>
        <span class="token property">display</span><span class="token punctuation">:</span> inline-block<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre></div><h3 id="_4-css3盒模型"><a href="#_4-css3盒模型" class="header-anchor">#</a> 4. CSS3盒模型</h3> <p>标准盒模型（<code>content-box</code>）、IE怪异盒模型（<code>border-box</code>）、<code>flex</code> 弹性伸缩盒模型、<code>column</code> 多列盒模型</p> <p>怪异盒模型的好处，固定到 <code>border</code> 控制宽高，不用重新计算 <code>padding</code> 和 <code>border</code></p> <p>Flex详见: <a href="http://www.ruanyifeng.com/blog/2015/07/flex-grammar.html" target="_blank" rel="noopener noreferrer">阮一峰的flex布局<span><svg xmlns="http://www.w3.org/2000/svg" aria-hidden="true" focusable="false" x="0px" y="0px" viewBox="0 0 100 100" width="15" height="15" class="icon outbound"><path fill="currentColor" d="M18.8,85.1h56l0,0c2.2,0,4-1.8,4-4v-32h-8v28h-48v-48h28v-8h-32l0,0c-2.2,0-4,1.8-4,4v56C14.8,83.3,16.6,85.1,18.8,85.1z"></path> <polygon fill="currentColor" points="45.7,48.7 51.3,54.3 77.2,28.5 77.2,37.2 85.2,37.2 85.2,14.9 62.8,14.9 62.8,22.9 71.5,22.9"></polygon></svg> <span class="sr-only">(opens new window)</span></span></a></p> <div class="language-scss extra-class"><pre class="language-scss"><code><span class="token selector">* </span><span class="token punctuation">{</span>
    <span class="token property">box-sizing</span><span class="token punctuation">:</span> content-box | border-box<span class="token punctuation">;</span> <span class="token comment">/* 影响因素有：content、padding、border、margin */</span>
<span class="token punctuation">}</span>
</code></pre></div><p><strong>JS如何设置获取盒模型对应的宽和高</strong></p> <ul><li><p>window.getComputedStyle(dom).width/height：兼容性更好、最优</p></li> <li><p>dom.style.width/height：只能获取到内敛样式的宽高</p></li> <li><p>dom.currentStyle.width/height：渲染以后的宽高，但只有IE兼容</p></li> <li><p>dom.getBoundingClientRect().width/height：主要用于计算一个元素相对于视窗左上角的绝对位置，有4个属性：top、left、width、height</p></li></ul> <p><strong>BFC</strong>-  解决边距重叠问题</p> <p>BFC概念：BFC就是块级格式化上下文。</p> <p>BFC原理：</p> <ol><li>BFC元素的垂直方向的边距会发生重叠</li> <li>BFC的区域不会与浮动元素的box重叠</li> <li>BFC元素是一个独立的容器，与外面的元素互不影响</li> <li>浮动元素也会参与计算BFC高度</li></ol> <p>解决方案，创建BFC:</p> <ul><li>overflow: hidden/auto;</li> <li>position: relative; // 不为static</li> <li>float: left | right; // 不为none</li> <li>display: inline-block、table、table-cell等</li></ul> <blockquote><p>清除浮动：父子元素同时设置float: left; 子级元素也会参与高度计算</p></blockquote> <p>BFC的使用场景：</p> <ul><li><p>列表上下间距，margin: 20px auto 10px;li之间应该间距30px，但实际只有20px，按最大数值重叠了</p></li> <li></li></ul> <h3 id="_5-几大经典布局"><a href="#_5-几大经典布局" class="header-anchor">#</a> 5. 几大经典布局</h3> <p>圣杯布局、双飞翼布局 =&gt; 左右固定，中间自适应</p> <ul><li>浮动 float</li> <li>定位：position</li> <li>表格：table</li> <li>弹性盒子模型：flex</li> <li>网格：grid</li></ul> <p>（1）圣杯布局：float和负margin</p> <div class="language-html extra-class"><pre class="language-html"><code><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">class</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>container clearfix<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span>
 <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">class</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>center<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>
 <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">class</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>left<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>
 <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">class</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>right<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>
</code></pre></div><div class="language-scss extra-class"><pre class="language-scss"><code><span class="token selector">html,
body </span><span class="token punctuation">{</span>
 <span class="token property">height</span><span class="token punctuation">:</span> 100%<span class="token punctuation">;</span>
 <span class="token property">overflow</span><span class="token punctuation">:</span> hidden<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token selector">.container </span><span class="token punctuation">{</span>
    <span class="token property">heigth</span><span class="token punctuation">:</span> 100%<span class="token punctuation">;</span>
    <span class="token property">padding</span><span class="token punctuation">:</span> 0 200px<span class="token punctuation">;</span>
    <span class="token selector">.left,
    .right </span><span class="token punctuation">{</span>
        <span class="token property">width</span><span class="token punctuation">:</span> 200px<span class="token punctuation">;</span>
        <span class="token property">min-height</span><span class="token punctuation">:</span> 200px<span class="token punctuation">;</span>
        <span class="token property">float</span><span class="token punctuation">:</span> left<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
    <span class="token selector">.center </span><span class="token punctuation">{</span>
        <span class="token property">width</span><span class="token punctuation">:</span> 100%<span class="token punctuation">;</span>
        <span class="token property">min-height</span><span class="token punctuation">:</span> 400px<span class="token punctuation">;</span>
        <span class="token property">float</span><span class="token punctuation">:</span> left<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
    <span class="token selector">.left </span><span class="token punctuation">{</span>
        <span class="token property">margin-left</span><span class="token punctuation">:</span> -100%<span class="token punctuation">;</span>
        <span class="token property">position</span><span class="token punctuation">:</span> relative<span class="token punctuation">;</span>
        <span class="token property">left</span><span class="token punctuation">:</span> -200px<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
    <span class="token selector">.right </span><span class="token punctuation">{</span>
        <span class="token property">margin-right</span><span class="token punctuation">:</span> -200px<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre></div><p>（2）双飞翼：</p> <div class="language-html extra-class"><pre class="language-html"><code><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">class</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>clearfix<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span>
 <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">class</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>container<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span>
  <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">class</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>center<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>
 <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>
 <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">class</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>left<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>
 <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">class</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>right<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>
</code></pre></div><div class="language-SCSS extra-class"><pre class="language-scss"><code><span class="token selector">html,
body </span><span class="token punctuation">{</span>
 <span class="token property">height</span><span class="token punctuation">:</span> 100%<span class="token punctuation">;</span>
 <span class="token property">overflow</span><span class="token punctuation">:</span> hidden<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token selector">.container,
.left,
.right </span><span class="token punctuation">{</span>
    <span class="token property">float</span><span class="token punctuation">:</span> left<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token selector">.container </span><span class="token punctuation">{</span>
    <span class="token property">width</span><span class="token punctuation">:</span> 100%<span class="token punctuation">;</span>
    <span class="token selector">.center </span><span class="token punctuation">{</span>
        <span class="token property">min-height</span><span class="token punctuation">:</span> 400px<span class="token punctuation">;</span>
        <span class="token property">margin</span><span class="token punctuation">:</span> 0 200px<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token selector">.left,
.right </span><span class="token punctuation">{</span>
    <span class="token property">width</span><span class="token punctuation">:</span> 200px<span class="token punctuation">;</span>
    <span class="token property">min-height</span><span class="token punctuation">:</span> 200px<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token selector">.left </span><span class="token punctuation">{</span>
    <span class="token property">margin-left</span><span class="token punctuation">:</span> -100%<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token selector">.right </span><span class="token punctuation">{</span>
    <span class="token property">margin-left</span><span class="token punctuation">:</span> -200px<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre></div><p>（3）使用calc</p> <div class="language-html extra-class"><pre class="language-html"><code>/* 以下方案全部用这种布局 */
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">class</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>container clearfix<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span>
 <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">class</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>left<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>
 <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">class</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>center<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>
 <span class="token tag"><span class="token tag"><span class="token punctuation">&lt;</span>div</span> <span class="token attr-name">class</span><span class="token attr-value"><span class="token punctuation attr-equals">=</span><span class="token punctuation">&quot;</span>right<span class="token punctuation">&quot;</span></span><span class="token punctuation">&gt;</span></span><span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>
<span class="token tag"><span class="token tag"><span class="token punctuation">&lt;/</span>div</span><span class="token punctuation">&gt;</span></span>
</code></pre></div><div class="language-scss extra-class"><pre class="language-scss"><code><span class="token selector">.container </span><span class="token punctuation">{</span>
 <span class="token selector">.left,
 .center,
 .right </span><span class="token punctuation">{</span>
  <span class="token property">float</span><span class="token punctuation">:</span> left<span class="token punctuation">;</span>
 <span class="token punctuation">}</span>
 <span class="token selector">.center </span><span class="token punctuation">{</span>
        <span class="token property">width</span><span class="token punctuation">:</span> <span class="token function">calc</span><span class="token punctuation">(</span>100% <span class="token operator">-</span> 400px<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">/* 兼容IE+，需要计算，不推荐 */</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre></div><p>（4）使用flex</p> <div class="language-scss extra-class"><pre class="language-scss"><code><span class="token selector">html,
body </span><span class="token punctuation">{</span>
 <span class="token property">height</span><span class="token punctuation">:</span> 100%<span class="token punctuation">;</span>
 <span class="token property">overflow</span><span class="token punctuation">:</span> hidden<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token selector">.container </span><span class="token punctuation">{</span>
 <span class="token property">display</span><span class="token punctuation">:</span> flex<span class="token punctuation">;</span>
 <span class="token property">justify-content</span><span class="token punctuation">:</span> space-between<span class="token punctuation">;</span>
 <span class="token property">height</span><span class="token punctuation">:</span> 100%<span class="token punctuation">;</span>
 <span class="token selector">.left,
 .right </span><span class="token punctuation">{</span>
  <span class="token property">flex</span><span class="token punctuation">:</span> 0 0 200px<span class="token punctuation">;</span>
 <span class="token punctuation">}</span>
 <span class="token selector">.center </span><span class="token punctuation">{</span>
        <span class="token property">flex</span><span class="token punctuation">:</span> 1<span class="token punctuation">;</span>
        <span class="token property">min-height</span><span class="token punctuation">:</span> 400px<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre></div><p>（5）定位</p> <div class="language-scss extra-class"><pre class="language-scss"><code><span class="token selector">html,
body </span><span class="token punctuation">{</span>
 <span class="token property">height</span><span class="token punctuation">:</span> 100%<span class="token punctuation">;</span>
 <span class="token property">overflow</span><span class="token punctuation">:</span> hidden<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token selector">.container </span><span class="token punctuation">{</span>
 <span class="token property">height</span><span class="token punctuation">:</span> 100%<span class="token punctuation">;</span>
 <span class="token property">position</span><span class="token punctuation">:</span> relative<span class="token punctuation">;</span>
 <span class="token selector">.left,
 .right </span><span class="token punctuation">{</span>
  <span class="token property">width</span><span class="token punctuation">:</span> 200px<span class="token punctuation">;</span>
  <span class="token property">min-height</span><span class="token punctuation">:</span> 200px<span class="token punctuation">;</span>
  <span class="token property">position</span><span class="token punctuation">:</span> absolute<span class="token punctuation">;</span>
  <span class="token property">top</span><span class="token punctuation">:</span> 0<span class="token punctuation">;</span>
 <span class="token punctuation">}</span>
 <span class="token selector">.left </span><span class="token punctuation">{</span>
  <span class="token property">left</span><span class="token punctuation">:</span> 0<span class="token punctuation">;</span>
 <span class="token punctuation">}</span>
 <span class="token selector">.right </span><span class="token punctuation">{</span>
  <span class="token property">right</span><span class="token punctuation">:</span> 0<span class="token punctuation">;</span>
 <span class="token punctuation">}</span>
 <span class="token selector">.center </span><span class="token punctuation">{</span>
        <span class="token property">min-height</span><span class="token punctuation">:</span> 400px<span class="token punctuation">;</span>
        <span class="token property">margin</span><span class="token punctuation">:</span> 0 200px<span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre></div><h3 id="_6-移动端响应式布局解决方案"><a href="#_6-移动端响应式布局解决方案" class="header-anchor">#</a> 6. 移动端响应式布局解决方案</h3> <ul><li>media: 媒体查询。一套方案 —— 常用</li> <li>rem: 应用于两套中的移动端 —— 常用</li> <li>flex: CSS3弹性盒子，不兼容IE</li> <li>vw/vh: 将视口分为100份</li></ul> <h3 id="_7-z-index-的工作原理"><a href="#_7-z-index-的工作原理" class="header-anchor">#</a> 7. z-index 的工作原理</h3> <p>考察：文档流、定位</p> <blockquote><p>z-index 属性指定一个元素的堆叠顺序。</p> <p>用法：z-index : auto | number</p></blockquote> <ol><li>z-index这个属性控制着元素在z轴上的表现形式。</li> <li>适用范围：仅适用于定位元素，即拥有relative,absolute,fixed属性的position元素。</li> <li>堆叠顺序是当前元素位于z轴上的值，数值越大说明元素的堆叠顺序越高，越靠近用户。</li> <li>未定义时，后来居上，未定义z-index的属性，元素的堆叠顺序基于它所在的文档树。默认情况下，后来的元素的z-index的值越大。</li> <li>使用场景：</li></ol> <ul><li>网页两侧的浮动窗口（播放器，指定按钮，广告等）</li> <li>导航栏浮动置顶</li> <li>隐藏div实现弹窗功能（通过设置div定位和z-index控制div的位置和出现隐藏）</li></ul> <h3 id="_8-文字垂直居中且可自适应"><a href="#_8-文字垂直居中且可自适应" class="header-anchor">#</a> 8. 文字垂直居中且可自适应</h3> <p>如何使一个div里面的文字垂直居中，且该文字的大小根据屏幕大小自适应？</p> <p>文字大小自适应：rem方案。</p> <ol><li>设置行高：line-height：行高；text-align: center;</li> <li>行内块：display: inline-block; vertical-align: center; margin: 0 auto;</li> <li>table：父级：display: table; 子级：display: table-cell; vertical-align: center; margin: 0 auto;</li> <li>定位：position + margin + inline-block/block.</li> <li>flex：优选。display: flex; justify-content: center; align-items: center;</li></ol> <h3 id="_9-css渲染性能"><a href="#_9-css渲染性能" class="header-anchor">#</a> 9. CSS渲染性能</h3> <p>不考虑其它因素，下面哪种的渲染性能更高？</p> <div class="language-scss extra-class"><pre class="language-scss"><code>.box a <span class="token punctuation">{</span>...<span class="token punctuation">}</span> <span class="token comment">/* 从右向左找，先找a，再找.box，进行了二次查找，会更慢 */</span>
a <span class="token punctuation">{</span>...<span class="token punctuation">}</span> <span class="token comment">/* 更高：一次性找到 */</span>
</code></pre></div></div> <footer class="page-edit"><!----> <div class="last-updated"><span class="prefix">更新时间:</span> <span class="time">12/1/2021, 4:31:04 PM</span></div></footer> <div class="page-nav"><p class="inner"><span class="prev">
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